DARPA is asking universities for access to their tunnels ASAP, and it's because the US military thinks its next war will go underground

A soldier with the 10th Mountain Division guards a hallway during training for subterranean warfare.SSG James Avery/US Army

The Defense Advanced Research Projects Agency (DARPA) tweeted
on Wednesday that it was seeking "university-owned or
commercially managed underground urban tunnels & facilities
able to host research & experimentation," raising concern
from Twitter users.

The agency told Insider that the request was also related to
its SubT Challenge, where teams of researchers show off
technology they develop to assist in searching, mapping, and
navigating underground spaces.

The agency noted the short notice of the request - it asked for
responses within two days - and specified
that it was seeking "a human-made underground environment
spanning several city blocks" which includes "a complex layout
& multiple stories, including atriums, tunnels &
stairwells."

While the Trump administration is increasingly looking to the skies and pressing for a Space Force, DARPA is focusing on operations underground.

Stacy Smenos, Dugway Proving Ground / DVIDS

In the agency's
online request for information, DARPA specifies that it's
trying to understand how technology could be used for rapid
mapping, search, and navigation operations, likely in the case of
urban conflict or disaster-related search-and-rescue operations.

The request comes out ahead of DARPA's Subterranean Challenge.

Matt Gonzales / US Marine Corps / DVIDS

The Subterranean Challenge, or SubT Challenge, invites teams of
researchers from all over the world to compete and find
technological solutions for underground operations. The teams use
locations - like the ones DARPA requested information about - to
test technologies that can search and navigate in underground
terrain where it might be too difficult for humans to go.

Teams in the systems
competition focus on technology like robotics that can
physically search and navigate in an underground terrain. On the
virtual track, teams compete and develop software that can be
used to assist in simulations of underground operations.

The urban circuit of the SubT challenge will take place in February 2020, hence the request for urban underground space.

Capt. Scott Kuhn / DVIDS

"As teams prepare for the
SubT Challenge Urban Circuit, the program recognizes it can
be difficult for them to find locations suitable to test their
systems and sensors," Adams told Insider.

"DARPA issued this RFI in part to help identify potential
representative environments where teams may be able to test in
advance of the upcoming event."

The military has become more aware that it needs to develop technology and strategy to fight in an underground, urban setting.

Sgt. Jessica DuVernay / DVIDS

Historically, underground warfare has been the domain of special
operations troops like Navy SEALs. But military researchers
predict that this kind of warfare will be too much for special
operators alone to navigate, particularly if dealing with an
adversary like China or Russia, which both have extensive
underground space. China in particular uses vast underground
complexes to store missiles and its nuclear arsenal.

"We did recognize, in a megacity that has underground facilities
- sewers and subways and some of the things we would encounter
... we have to look at ourselves and say 'OK, how does our
current set of equipment and our tactics stack up?'" Col. Townley
Hedrick, commandant of the infantry school at the Army's Maneuver
Center of Excellence at Fort Benning, Georgia, said
in an interview with Military.com last year.

The military has encountered underground facilities before — some Vietnam War-era special units explored tunnels dug by the Viet Cong.